The present invention relates generally to shift systems for transmissions and transfer cases of the type used in the driveline of motor vehicles. Specifically, the present invention is directed to a spring-loaded shift fork assembly for use in such shift systems.
It is known in the automobile industry to equip power transfer assemblies (i.e., manual transmissions, transfer cases, etc.) with a shift system having spring-loaded shift devices for completing a delayed gear or mode shift once speed synchronization or a torque break occurs. Examples of conventional spring-loaded shift systems are disclosed in U.S. Pat. Nos. 4,529,080, 4,770,280 and 5,517,876. In each of these patents, a pair of springs are used to provide a bi-directional preload function for effectuating coupling of a dog-type shift sleeve with a desired gearset. While such arrangements are satisfactory for their intended purpose, a need exists to develop simpler, more cost-effective alternatives that provide the desired function while advancing the art.
Accordingly, it is an object of the present invention to provide an improved shift system for a power transmission device having a spring-loaded shift fork assembly.
As a related object, the shift system of the present invention is adapted for use with the range shift mechanism of a four-wheel drive transfer case.
As a still further object, the shift system of the present invention is adapted for use with a gearshift mechanism of a multi-speed transmission or transaxle.
According to a preferred embodiment of the present invention, a shift system for a transfer case includes a spring-load range fork assembly operable for shifting a range sleeve between two speed range positions. The range fork assembly includes a bracket, a range fork, and a spring assembly. The spring assembly is compressed and inserted into chambers formed in both the bracket and range fork. The range fork assembly is slidably maintained on a shift rail and the range fork is coupled to the range sleeve. An actuator mechanism is provided for causing selective axial movement of the range fork assembly on the rail. During operation of the transfer case, the transmission of drive torque while shifting into either speed range may create a resistance force which impedes the axial movement of the range sleeve. However, the spring assembly allows the bracket to shift and apply a shift force on the range fork. When a torque reversal occurs, the shift force causes the range fork to slide the range sleeve to the desired position.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.